What causes weightlessness in space despite gravity?

Weightlessness in space is caused by the continuous free-fall towards Earth, creating the sensation of zero gravity.

In more detail, it's important to understand that gravity is still present in space, even on the International Space Station (ISS). The force of gravity decreases with distance, but it doesn't completely disappear. Astronauts aboard the ISS are still subject to about 90% of the Earth's gravity. So, why do they appear weightless?

The answer lies in the concept of free-fall. When an object is in free-fall, it is falling towards the Earth due to gravity, but it's also moving forward fast enough to keep missing it. This is exactly what's happening with the ISS and its inhabitants. They're falling towards the Earth, but they're also moving forward at a speed of about 28,000 kilometres per hour. This forward motion is enough to keep them from hitting the Earth as they fall.

This continuous falling is what creates the sensation of weightlessness. When you're in free-fall, you don't feel the force of gravity pulling you down. Instead, you feel weightless. This is the same sensation you experience when you go over the top of a hill on a roller coaster, or when you jump off a diving board. It's not that gravity has disappeared, but rather that you're falling at the same rate as everything around you, so you don't feel its effects.

In essence, weightlessness in space is not due to the absence of gravity, but rather the result of being in a state of continuous free-fall. This is a common misconception, but understanding the physics behind it can help clarify why astronauts appear to float in space. It's not that they're beyond the reach of Earth's gravity, but rather that they're falling towards Earth in such a way that they feel weightless.